It looks like I have a problem with either the filler hose or the breather pipe that comes off the other side of the tank. When I fill up to the point the pump cuts out, fuel drips down onto the garage forecourt. Trouble is I can't find out exactly where the leak is coming from as everything on top of the tanks appears dry. All the joints I've been able to see or touch seem okay. Dabbing with a piece of tissue hasn't revealed any leaks. Other than diving under the car while the wife fills her up, what should I try next.
NOTE: There is no leakage after I fill up and stop the vehicle after a mile or two

If it’s ‘only’ leaking when you fill up (and engine off I assume?), then to me it would suggest it’s not related to the return side, so presumably something on the fill side. There is a vent pipe, but that would only vent air out.
Maybe in the main filler pipe?

Wouldn’t be messing around on the forecourt, but if you were to fill up and go home, then get someone to use a jerry can to keep topping it up while you look closer - might be doable?
Just a thought - if you’re going to do that, drive it up onto 4 lumps of scaffold boards (on each corner) or something, to gain the height to get under it. Jacking it up will give you a potential wild goose chase due to not being level front/back or left/right!

Freddie17 said:

Just a thought - if you’re going to do that, drive it up onto 4 lumps of scaffold boards (on each corner) or something, to gain the height to get under it. Jacking it up will give you a potential wild goose chase due to not being level front/back or left/right!

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Good point. I've only got a pair of axle stands.

Rank Amatuer said:

Good point. I've only got a pair of axle stands.

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A (good) railway sleeper , cut into 4, works really well for some quick ground clearance. Just drive that baby right on up for an instant 4” lift …

Of course, elf n safety dictates that I should say “place your axle stands when stopped, for added protection”, ‘cos railway sleepers have a habit of rapidly falling apart (not)

From a safety and elf perspective, wear some cushioning protective layer on your forehead.

Cos when the diesel drops down into your eyes, your head will flinch up and hit the underbody.

Alternatively, wear eye protection as that will have the added benefit of protecting your eyesight.

BTW, do you see any fuel around the filler?

Some of the vehicles we have at work have a drain from around the filler area. When the AdBlue spills (its filler in under the same cover as the diesel), it drains out under the vehicle.

Wondering if you have some kind of small blockage at the top of the filler that is causing fuel to splash about up there and run out this possible/hypothetical drain. Possibly that little pipe that HD2 is clipping to in the diagram you posted.